Process for the preparation of cyclohexanone oxime

ABSTRACT

The invention relates to a process for the production of cyclohexanone oxime in which a phosphate-containing aqueous reaction medium is cycled from a hydroxylammonium synthesis zone to a cyclohexanone oxime synthesis zone and back to the hydroxylammonium synthesis zone, in which hydroxylammonium synthesis zone hydroxylammonium is formed by catalytic reduction of nitrate with hydrogen, and in which cyclohexanone oxime synthesis zone hydroxylammonium is reacted with cyclohexanone to form cyclohexanone oxime, the cyclohexanone and an organic solvent being fed into the cyclohexanone oxime synthesis zone, an organic medium comprising the organic solvent and cyclohexanone oxime being withdrawn from the cyclohexanone oxime synthesis zone, characterized in that the ratio f h /f c &lt;1.00 wherein  
     f h  represents the molar quantity of hydroxylammonium fed to the cyclohexanone oxime synthesis zone per unit of time (in mol/s), and  
     f c  represents the molar quantity of cyclohexanone fed to the cyclohexanone oxime synthesis zone per unit of time (in mol/s).

[0001] The present invention relates to a process for the production ofcyclohexanone oxime in which a phosphate-containing aqueous reactionmedium is cycled from a hydroxylammonium synthesis zone to acyclohexanone oxime synthesis zone and back to the hydroxylammoniumsynthesis zone, in which hydroxylammonium synthesis zonehydroxylammonium is formed by catalytic reduction of nitrate withhydrogen, and in which cyclohexanone oxime synthesis zonehydroxylammonium is reacted with cyclohexanone to form cyclohexanoneoxime, the cyclohexanone and an organic solvent being fed into thecyclohexanone oxime synthesis zone, an organic medium comprising theorganic solvent and cyclohexanone oxime being withdrawn from thecyclohexanone oxime synthesis zone.

[0002] Oximes can be produced in a process in which a buffered, aqueousreaction medium containing buffer acids or acidic salts, for examplephosphate buffers, and buffer salts derived from these acids, iscontinuously recycled between a hydroxylammonium synthesis zone in whichnitrate ions are catalytically reduced with molecular hydrogen tohydroxylammonium, and an oximation zone where a ketone, e.g.cyclohexanone, is converted to an oxime. Before the aqueous reactionmedium is passed into the hydroxylammonium synthesis zone, it may beenriched with the required nitrate ions by addition of nitric acid or byabsorption of nitrous gases in the aqueous reaction medium in whichinstance nitric acid is formed in situ. After having been enriched inhydroxylammonium in the hydroxylammonium synthesis zone, the aqueousreaction medium is then passed to the oxime synthesis zone, where thehydroxylammonium reacts with a ketone, e.g., cyclohexanone, forming thecorresponding oxime. The oxime can then be separated from the aqueousreaction medium which is recycled to the hydroxylammonium synthesiszone.

[0003] The net chemical reactions occurring during the process can berepresented by the following equations:

[0004] 1) Preparation of the hydroxylammonium:

2H₃PO₄+NO₃ ⁻+3H₂→NH₃OH⁺+2H₂PO₄ ⁻+2H₂O

[0005] 2) Preparation of the oxime

NH₃OH⁺+2H₂PO₄ ⁻+2H₂O+

═O

═N—OH+H₃PO₄+H₂PO₄ ⁻+3H₂O

[0006] 3) Supply of HNO₃ to make up the depletion of the source ofnitrate ions after removal of the oxime formed

H₂PO₄ ⁻+HNO₃→H₃PO₄+NO₃ ⁻

[0007] The catalyst used in the reduction of the nitrate ions isgenerally palladium and/or platinum on a carrier material of carbon oralumina, the carrier material being loaded with from 1 to 25% wt. ofpalladium and/or platinum. The activity of the catalyst is adverselyaffected by the presence of organic contaminants, such as the ketone andoxime, in the recycled stream.

[0008] A number of techniques have been developed to address thisproblem of the recycled stream containing high amounts of contaminantsthat poison the catalyst. U.S. Pat. No. 3,940,442 describes thatpoisoning of the catalyst is prevented by heating the aqueous reactionmedium being recycled from the cyclohexanone oxime synthesis zone to thehydroxylammonium synthesis zone to an elevated temperature in the rangeof 50° C. to 106° C. GB-A-1,283,894 and U.S. Pat. No. 3,997,607 describethat heat treating the aqueous reaction medium in the presence ofnitrous acid, respectively nitrous gases reduce the extent of catalystpoisoning.

[0009] It has now been found that a decreased molar ratio of(hydroxylammonium fed to the cyclohexanone oxime synthesis zone per unitof time)/(cyclohexanone fed to the cyclohexanone oxime synthesis zoneper unit of time) results in a decrease of the concentration of theorganic contaminants in the aqueous reaction medium which is recycledfrom the cyclohexanone oxime synthesis zone to the hydroxylammoniumsynthesis zone. Therefore, the invention provides a process for theproduction of cyclohexanone oxime in which a phosphate-containingaqueous reaction medium is cycled from a hydroxylammonium synthesis zoneto a cyclohexanone oxime synthesis zone and back to the hydroxylammoniumsynthesis zone, in which hydroxylammonium synthesis zonehydroxylammonium is formed by catalytic reduction of nitrate withhydrogen, and in which cyclohexanone oxime synthesis zonehydroxylammonium is reacted with cyclohexanone to form cyclohexanoneoxime, the cyclohexanone and an organic solvent being fed into thecyclohexanone oxime synthesis zone, an organic medium comprising theorganic solvent and cyclohexanone oxime being withdrawn from thecyclohexanone oxime synthesis zone, characterized in that the ratiof_(h)/f_(c)<1.00 wherein f_(h) represents the molar quantity ofhydroxylammonium fed to the cyclohexanone oxime synthesis zone per unitof time (in mol per unit of time), and f_(c) represents the molarquantity of cyclohexanone fed to the cyclohexanone oxime synthesis zoneper unit of time (in mol per unit of time). The invention also providesa process for the production of cyclohexanone oxime in which (i) anaqueous reaction medium containing hydroxylammonium, phosphate andnitrate, (ii) cyclohexanone and (iii) an organic solvent are fed into acyclohexanone oxime synthesis zone, in which hydroxylammonium is reactedwith cyclohexanone to form cyclohexanone oxime, an organic mediumcomprising the organic solvent and cyclohexanone oxime being withdrawnfrom the cyclohexanone oxime synthesis zone, characterized in thatcharacterized in that the ratio f_(h)/f_(c)<1.00.

[0010] Using the process according to the invention, it is possible todecrease the amount of organic contaminants which poison the catalyst,in particular residual cyclohexanone and/or cyclohexanone oxime,entering the hydroxylammonium synthesis zone under further equalcircumstances. According to the invention it is also possible to omitsteps for the removal of organic contaminants or to lessen the extent towhich such steps are carried out, for instance by using smallerequipment, the ratio f_(h)/f_(c)<1.00 avoiding or mitigating an increaseof the amount of organic contaminants entering the hydroxylammoniumsynthesis zone. According to the invention, it is also possible toincrease the concentration cyclohexanone oxime in the organic mediumexiting the cyclohexanone oxime synthesis zone, the ratiof_(h)/f_(c)<1.00 avoiding or mitigating an increase of the amount oforganic contaminants entering the hydroxylammonium synthesis zone.

[0011] It is noted that GB-A-1,138,750 describes a process for theproduction of cyclohexanone oxime in which an aqueous reaction mediumcontaining phosphate and hydroxylammonium obtained in a hydroxylammoniumsynthesis zone is cycled to a cyclohexanone oxime synthesis zonetogether with cyclohexanone and toluene. In the known process, the ratiof_(h)/f_(c) is equal to 1.00. It is not disclosed that decreasing saidratio results in a decrease of the concentration of organic contaminantsin the aqueous reaction medium which is recycled from the cyclohexanoneoxime synthesis zone to the hydroxylammonium synthesis zone.

[0012] According to the invention, the ratio f_(h)/f_(c)<1.00.Preferably, the ratio f_(h)/f_(c)<0.99, more preferably less than 0.98,in particular lower than 0.97. These decreased ratios result in afurther decrease of the concentration of organic contaminants in theaqueous reaction medium exiting the cyclohexanone oxime synthesis. Thereis no specific lower limit for the ratio f_(h)/f_(c). The ratiof_(h)/f_(c) is generally higher than 0.5, preferably higher than 0.7,more preferably higher than 0.8.

[0013] In the cyclohexanone oxime synthesis zone, hydroxylammonium isreacted with cyclohexanone to form cyclohexanone oxime. Preferably, theaqueous reaction medium and a stream comprising the cyclohexanone andthe organic solvent are contacted in countercurrent flow. This is a veryeffective way of separating cyclohexanone oxime from the aqueousreaction medium, A suitable process is for instance described inGB-A-1,138,750. Use may be made of known types of counterflow reactors,such as for instance pulsed columns filled with packing bodies orrotating disc reactors. It is also possible to use a system comprising anumber, e.g. 3 to 6, of series-connected reactors equipped withstirrers, each of these reactors also being provided with aliquid-liquid separator. Preferably, the organic solvent has asolubility in water of less than 0.1% by weight at 20° C. Preferably,the organic solvent is selected from the group consisting of benzene,toluene, xylene, methylcyclopentane, cyclohexane and mixtures thereof.Most preferably, the organic solvent is toluene. Preferably, thecyclohexanone is dissolved in the organic solvent.

[0014] There is no specific lower limit for the concentrationcyclohexanone oxime in the organic medium exiting the cyclohexanoneoxime synthesis zone. Generally, the cyclohexanone oxime concentrationin the organic medium exiting the cyclohexanone oxime synthesis zone ishigher than 5 wt. %. An increased cyclohexanone oxime concentration inthe organic medium exiting the cyclohexanone oxime synthesis zone hasthe advantage that separation of the organic solvent from thecyclohexanone oxime, for instance in a distillation process, can becarried out using less energy. Preferably, the cyclohexanone oximeconcentration in the organic medium exiting the oxime synthesis zone ishigher than 25 wt. %, more preferably higher than 30 wt. %, inparticular higher than 35 wt. %, more in particular higher than 38 wt.%. An increased concentration cyclohexanone oxime may for instance beachieved by reducing the flow rate of the solvent into the oximesynthesis zone relative to the flow rate of the cyclohexanone into theoxime synthesis zone. Generally, the cyclohexanone oxime concentrationin the organic medium exiting the cyclohexanone oxime synthesis zone, islower than 95 wt. %, preferably lower than 80 wt. %, more preferablylower than 60 wt. %. All cyclohexanone oxime concentrations in theorganic medium are given relative to the sum weight of the cyclohexanoneoxime plus organic solvent.

[0015] Typically, the joint content of the cyclohexanone andcyclohexanone oxime in the aqueous reaction medium exiting thecyclohexanone oxime synthesis zone is below 0.2 wt. % (2000 ppm),preferably below 0.1 wt. %, more preferably below 0.05 wt. %, inparticular below 0.02 wt. %, more in particular below 0.01 wt. %, mostpreferably below 0.005 wt. % (relative to the weight of the aqueousreaction medium).

[0016] We have found that an increase of the concentration cyclohexanoneoxime in the organic medium exiting the cyclohexanone oxime synthesiszone may result in an increase of the concentration of organiccontaminants in the aqueous reaction medium exiting the hydroxylammoniumsynthesis zone. The process according to the invention has the advantagethat this effect is mitigated or avoided.

[0017] The cyclohexanone oxime synthesis zone may be operated at atemperature ranging from 40 to 150° C. and at atmospheric,sub-atmospheric, or elevated pressures, preferably between 0.05 and 0.5MPa, more preferably between 0.1 and 0.2 MPa, most preferably between0.1 and 0.15 MPa. Preferably, the aqueous reaction medium entering thecyclohexanone oxime synthesis zone has a pH of between 1 and 6, morepreferably between 1.5 and 4.

[0018] There is no specific lower limit for the concentrationhydroxylammonium in the aqueous reaction medium entering thecyclohexanone oxime synthesis zone. Generally, the concentrationhydroxylammonium in the aqueous reaction medium entering thecyclohexanone oxime synthesis zone is higher than 0.7 mol/l. Anincreased concentration of hydroxylammonium is advantageous, since theconversion of hydroxylammonium in the cyclohexanone oxime synthesis zonemay then be increased. Furthermore, the amount of cyclohexanone oximeproduced per unit of time can be increased by increasing theconcentration hydroxylammonium in the aqueous reaction medium enteringthe cyclohexanone oxime synthesis zone. Preferably, the concentrationhydroxylammonium in the aqueous reaction medium entering thecyclohexanone oxime synthesis zone is higher than 0.8 mol/l, morepreferably higher than 1.0 mol/l, in particular higher than 1.2 mol/l,more in particular higher than 1.4 mol/l, most preferably higher than1.6 mol/l. An increased concentration hydroxylammonium in the aqueousreaction medium entering the cyclohexanone oxime synthesis zone may forinstance be achieved by increasing the residence time in thehydroxylammonium synthesis zone and/or by increasing the nitrateconcentration in the aqueous reaction medium entering thehydroxylammonium synthesis zone. There is no specific upper limit forthe concentration hydroxylammonium in the aqueous reaction mediumentering the cyclohexanone oxime synthesis zone. Generally, theconcentration hydroxylammonium in the aqueous reaction medium enteringthe cyclohexanone oxime synthesis zone is below 2.5 mol/l.

[0019] We have found that an increase of the concentrationhydroxylammonium in the aqueous reaction medium entering thecyclohexanone oxime systhesis zone may result in an increase of theconcentration of organic contaminants in the aqueous reaction mediumexiting the cyclohexanone oxime synthesis zone. The process according tothe invention has the advantage that this effect is mitigated oravoided.

[0020] The aqueous reaction medium contains phospate. Generally, thephosphate concentration in the aqueous reaction medium entering thecyclohexanone oxime synthesis zone is higher than 2.0 mol/l, preferablyhigher than 2.5 mol/l, more preferably higher than 3.0 mol/l, inparticular higher than 3.3 mol/l, more in particular higher than 3.5mol/l, most preferably higher than 3.7 mol/l. We have found thatincreasing the phosphate concentration in the aqueous reaction mediumentering the cyclohexanone oxime synthesis zone is advantageous since itresults in a decrease of the concentration of organic contaminants inthe aqueous reaction medium exiting the cyclohexanone oxime synthesiszone. Preferably, the phosphate concentration is chosen such that nocrystallization occurs, which depends, inter alia, on the temperatureand the concentration of other components in the aqueous reactionmedium. Generally, the phosphate concentration in the aqueous reactionmedium entering the cyclohexanone oxime synthesis zone is lower than 8mol/l, preferably lower than 5 mol/l, more preferably lower than 4.5mol/l. As used herein, the phosphate concentration denotes the sumconcentration of all phosphates, irrespective of the form in which theyare present, expressed in mol per liter of aqueous reaction reactionmedium. Preferably, the phosphates are present as PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄⁻, H₃PO₄, salts of PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻, and/or combinationsthereof.

[0021] In a preferred embodiment, the cyclohexanone oxime synthesis zonecomprises a reaction zone in which hydroxylammonium is reacted withcyclohexanone to form cyclohexanone oxime by contacting the aqueousreaction medium and the stream comprising the cyclohexanone and theorganic solvent in countercurrent flow, and an extraction zone in whichthe aqueous reaction medium and an organic solvent are contacted,preferably in countercurrent flow, the aqueous reaction medium enteringthe cyclohexanone oxime synthesis zone being fed to the reaction zone,the aqueous reaction medium exiting the reaction zone being fed to theextraction zone. This embodiment has the advantage that organicresiduals, in particular cyclohexanone and cyclohexanone oxime, areseparated from the aqueous reaction medium exiting the reaction zone.Preferably, cyclohexanone is fed to the oxime synthesis zone between thereaction zone and the extraction zone. Preferably, organic solventexiting the extraction zone is fed to the reaction zone. Preferably,cyclohexanone is fed to the cyclohexanone oxime synthesis zone in theorganic solvent entering the extraction zone. Use may be made of knowntypes of extractors such as for instance an extraction column, or one ormore reactors equipped with stirrers, optionally series-connected, eachof these reactors also being provided with a liquid-liquid separator.Preferably, a pulsed column filled with packing bodies is used. Thereaction zone and extraction zone are preferably operated at atemperature ranging from 40 to 150° C. and at atmospheric,subatmospheric, or elevated pressures, preferably between 0.05 and 0.5MPa, more preferably between 0.1 and 0.2 MPa, most preferably between0.1 and 0.15 MPa. Use may be made of known types of extractors such asfor instance extraction columns, preferably, pulsed columns filled withpacking bodies, or one or more reactors equipped with stirrers,optionally series-connected, each of these reactors also being providedwith a liquid-liquid separator. Preferably, the organic solvent has asolubility in water of less than 0.1% by weight at 20° C. Preferably,the organic solvent is selected from the group consisting of benzene,toluene, xylene, methylcyclopentane, cyclohexane and mixtures thereof.Most preferably, the organic solvent is toluene. The operatingconditions for the reaction zone and the extraction zone are notnecessarily the same. Preferably, the same solvent is used in thereaction zone and the extraction zone. Preferably, the joint content ofthe cyclohexanone and cyclohexanone oxime in the aqueous reaction mediumexiting the extraction zone is below 0.2 wt. % (2000 ppm), morepreferably below 0.05 wt. %, in particular below 0.02 wt. %, more inparticular below 0.01 wt. %, most preferably below 0.005 wt. % (relativeto the weight of the aqueous reaction medium).

[0022] Preferably, the aqueous reaction medium exiting the cyclohexanoneoxime synthesis zone or exiting the extraction zone is subjected tostripping to achieve further reduction in organic contaminants. Thestripping process described in U.S. Pat. No. 3,940,442 may for instancebe used. It is preferred that the joint content of cyclohexanone andcyclohexanone in the aqueous reaction medium entering thehydroxylammonium synthesis zone is not more than 0.02 wt. % (200 ppm),more preferably not more than 0.005 wt. %, in particular not more than0.002 wt. %, more in particular not more than 0.001 wt. % and mostpreferably not more than 0.0002 wt. % (relative to the weight of theaqueous reaction medium).

[0023] Generally, the aqueous reaction medium is an acidic, bufferedreaction medium. The aqueous reaction medium may contain ammonium (NH₄⁺), for instance formed as a by-product in the synthesis ofhydroxylammonium. Preferably, in the aqueous reaction medium enteringthe cyclohexanone oxime synthesis zone, the ratio c(NH₄ ⁺)/c(phosphate)is between 0.1 and 3, more preferably between 0.2 and 2, most preferablybetween 0.5 and 1.5, wherein c(NH₄ ⁺) represents the concentration ofNH₄ ⁺ in mol/l and c(phosphate) represents the phosphate concentrationin mol/l.

[0024] Generally, the aqueous reaction medium entering the cyclohexanoneoxime synthesis zone contains nitrate (NO₃ ⁻). Preferably, in theaqueous reaction medium entering the cyclohexanone oxime synthesis zone,the c(NO₃ ⁻)/c(phosphate) is between 0.05 and 1, more preferably between0.1 and 0.5, wherein c(NO₃ ⁻) represents the concentration of NO₃ ⁻ inmol/l and c(phosphate) represents the phosphate concentration in mol/l.

[0025] In the hydroxylammonium synthesis zone hydroxylammonium is formedby catalytic reduction of nitrate with hydrogen. The hydroxylammoniumsynthesis zone may be operated at a temperature ranging from 20 to 100°C., preferably 30-90° C., more preferably 40-65° C., and at atmospheric,sub-atmospheric or elevated pressures, preferably between 0.1 and 5 MPa,more preferably between 0.3 and 3 MPa, and in particular between 0.5 and2 MPa (hydrogen partial pressure). Preferably, the pH in thehydroxylammonium synthesis zone is between 0.5 and 6, more preferablybetween 1 and 4. The catalyst employed in this zone is generally presentin a range of between 1 to 25 wt. %, preferably between 5 to 15 wt. % ofa precious metal, relative to total weight of support plus catalyst.Preferably, the catalyst is a palladium containing catalyst, forinstance a palladium or a palladium-platinum catalyst, present on asupport, such as for instance carbon or alumina support. Generally, thecatalyst is present in the hydroxylammonium synthesis zone in an amountof 0.2-5 wt. % relative to the total liquid weight in thehydroxylammonium reactor vessel(s).

BRIEF DESCRIPTION OF THE DRAWING

[0026]FIG. 1 is a schematic diagram of an embodiment of the processaccording to the present invention.

DESCRIPTION OF AN EMBODIMENT

[0027] Referring to FIG. 1, A represents the hydroxylammonium synthesiszone. A cyclohexanone oxime synthesis zone is used comprising reactionzone B and extraction zone C. To zone A, containing catalyst, hydrogenis fed via line 1; unreacted hydrogen is discharged, with any othergases, via line 2. The aqueous reaction medium, containing, inter alia,phosphate, is fed to zone A through line 15 and after having beenenriched in hydroxylammonium (also ammonium as a by-product) in thehydroxylammonium synthesis zone, is passed to the reaction zone B vialine 3. The cyclohexanone to be converted is fed in an organic solventto the reaction zone B via line 4. The cyclohexanone is introduced intothe organic solvent via line 7. The ratio f_(h)/f_(c) is less than 1.00.The largest part of cyclohexanone oxime produced and dissolved in theorganic solvent is removed from the system via line 5.

[0028] Upon exiting reaction zone B, the aqueous reaction medium ispassed to extraction zone C via line 6. Upon exiting reaction zone B,the hydroxylammonium content of the aqueous reaction medium has beenreduced by reaction and contains small quantities of cyclohexanone andcyclohexanone oxime contaminants. The organic solvent enters extractionzone C through line 9. Within extraction zone C, additionalcyclohexanone oxime is removed from the aqueous reaction medium andcarried out of zone C in the organic solvent through line 8. In theextraction zone C, the residual organic contaminants(cyclohexanone+cyclohexanone oxime) in the aqeuous reaction medium isreduced.

[0029] The aqueous reaction medium exits extraction zone C through line10 which passes the aqueous reaction medium to a separation operation,stripping column D. In this column, cyclohexanone oxime is hydrolyzed tocyclohexanone and the cyclohexanone thus formed together with thecyclohexanone already present is discharged with other organic materialsand water (e.g., as an azeotrope) through line 11. The aqueous reactionmedium being recycled in the system then passes through line 12 to zoneE. In zone E, nitric acid is produced. Preferably, nitric acid isproduced, at zone E or thereafter, by reacting air fed through line 13with ammonia fed through line 14 and with water from the aqueousreaction medium. Directly supplying nitric acid to the aqueous reactionmedium instead of producing nitric acid is also possible. Accordingly,the nitrate level is increased in the inorganic medium in zone E. Inzone E, ammonium ions, e.g. formed as a by-product in the synthesis ofhydroxylammonium, may be converted by means of gases containing nitrogenoxides. However, other methods for removal of ammonium ions may also beused. The aqueous reaction medium then completes the cycle by returningto hydroxylammonium synthesis zone A via line 15. The process is cardedout continuously.

[0030] The following specific examples are to be construed as merelyillustrative, and not limitive, of the remainder of the disclosure.

EXAMPLES AND COMPARATIVE EXPERIMENTS Example 1

[0031] Cyclohexanone oxime was produced using the set-up as shown inFIG. 1.

[0032] In hydroxylammonium synthesis zone A (containing a catalyst (10wt. % Pd supported on carbon), operated at a temperature of 52° C. at apressure of 1 MPa (hydrogen partial pressure)) an aqueous reactionmedium was produced per unit of time having the following composition:

[0033] 1.28 mol NH₃OH.H₂PO₄

[0034] 1.33 mol NH₄H₂PO₄

[0035] 0.70 mol H₃PO₄

[0036] 1.86 mol NH₄NO₃

[0037] 39.6 mol H₂O

[0038] and fed (via line 3) to reaction zone B (a pulsed packed column,operated at 55° C.). Per unit of time 1.32 mol cyclohexanone was fed(via line 7) to zone B, resulting in a ratio f_(h)/f_(c) of 0.97. Perunit of time 1.25 mol cyclohexanone oxime (141.3 g) was formed. Per unitof time 251 g toluene was fed to extraction zone C, the cyclohexanoneoxime concentration in the organic medium (relative to the sum weight oftoluene plus cyclohexanone oxime) leaving zone B via line 5 being 36 wt.%. The aqueous reaction medium exiting zone B was fed to extraction zoneC (a pulsed packed column, operated at 70° C.). The resultingconcentration organic residuals (cyclohexanone+cyclohexanone oxime) inthe aqueous reaction medium exiting extraction zone C was 6 ppm (0.0006wt. %).

[0039] Comparative Experiment A

[0040] Example 1 was repeated. However, per unit of time 1.24 molcyclohexanone was fed to zone B, i.e. the ratio f_(h)/f_(c) was 1.03instead of 0.97. The flow rate of the toluene was adjusted such that thecyclohexanone oxime concentration in the organic medium (relative to thesum weight of toluene plus cyclohexanone oxime) was kept 36 wt. %. Theresulting concentration organic residuals (cyclohexanone+cyclohexanoneoxime) in the aqueous medium exiting extraction zone C was 21 ppm(0.0021 wt. %). When comparing example 1 and comparative experiment A,it is shown that an decrease of the ratio f_(h)/f_(c) to below 1.00according to the invention results in a decrease of the concentrationorganic residuals (cyclohexanone+cyclohexanone oxime).

[0041] Comparative Experiment B

[0042] Comparative experiment A was repeated. However, the flow rate ofthe toluene was decreased such that the concentration cyclohexanoneoxime dissolved in toluene withdrawn from zone B, was 42 wt. % (relativeto the sum weight of cyclohexanone plus cyclohexanone oxime). Theresulting concentration organic residuals (cyclohexanone+cyclohexanoneoxime) in the aqueous medium exiting extraction zone C was 356 ppm(0.0356 wt. %).

Example 2

[0043] Comparative experiment B was repeated. However, per unit of time1.32 mol cyclohexanone was fed to zone B, resulting in a ratiof_(h)/f_(c) of 0.97 instead of 1.03. The resulting concentration organicresiduals (cyclohexanone+cyclohexanone oxime) in the aqueous mediumexiting extraction zone C was 96 ppm (0.0096 wt. %). When comparingexample 2 and comparative experiment B, it is shown that a decrease ofthe ratio f_(h)/f_(c) to below 1.00 according to the invention resultsin a decrease of the concentration organic residuals(cyclohexanone+cyclohexanone oxime).

[0044] Particular embodiments of this invention have been illustratedand described above. However, those of ordinary skill in the artunderstand that various modifications can be made, without departingfrom the spirit and scope of the invention. Accordingly, interpretationof this invention should not be limited, except as by the appendedclaims.

1. Process for the production of cyclohexanone oxime in which aphosphate-containing aqueous reaction medium is cycled from ahydroxylammonium synthesis zone to a cyclohexanone oxime synthesis zoneand back to the hydroxylammonium synthesis zone, in whichhydroxylammonium synthesis zone hydroxylammonium is formed by catalyticreduction of nitrate with hydrogen, and in which cyclohexanone oximesynthesis zone hydroxylammonium is reacted with cyclohexanone to formcyclohexanone oxime, the cyclohexanone and an organic solvent being fedinto the cyclohexanone oxime synthesis zone, an organic mediumcomprising the organic solvent and cyclohexanone oxime being withdrawnfrom the cyclohexanone oxime synthesis zone, characterized in that theratio f_(h)/f_(c)<1.00 wherein f_(h) represents the molar quantity ofhydroxylammonium fed to the cyclohexanone oxime synthesis zone per unitof time, and f_(c) represents the molar quantity of cyclohexanone fed tothe cyclohexanone oxime synthesis zone per unit of time.
 2. Process forthe production of cyclohexanone oxime in which (i) an aqueous reactionmedium containing hydroxylammonium, phosphate and nitrate, (ii)cyclohexanone and (iii) an organic solvent are fed into a cyclohexanoneoxime synthesis zone, in which hydroxylammonium is reacted withcyclohexanone to form cyclohexanone oxime, an organic medium comprisingthe organic solvent and cyclohexanone oxime being withdrawn from thecyclohexanone oxime synthesis zone, characterized in that characterizedin that the ratio f_(h)/f_(c)<1.00 wherein f_(h) represents the molarquantity of hydroxylammonium fed to the cyclohexanone oxime synthesiszone per unit of time f_(c) represents the molar quantity ofcyclohexanone fed to the cyclohexanone oxime synthesis zone per unit oftime.
 3. Process according to claim 1 or claim 2, characterized in thatthe ratio f_(h)/f_(c)<0.99.
 4. Process according to claim 3,characterized in that the ratio f_(h)/f_(c)<0.98.
 5. Process accordingto any one of claims 1 to 4, characterized in that the cyclohexanoneoxime concentration in the organic medium exiting the cyclohexanoneoxime synthesis zone is higher than 25 wt. %.
 6. Process according toclaim 5, characterized in that the cyclohexanone oxime concentration inthe organic medium exiting the cyclohexanone oxime synthesis zone ishigher than 30 wt. %.
 7. Process according to claim 6, characterized inthat the cyclohexanone oxime concentration in the organic medium exitingthe cyclohexanone oxime synthesis zone is higher than 35 wt. %. 8.Process according to any one of claims 1 to 7, characterized in that theconcentration hydroxylammonium in the aqueous reaction medium enteringthe cyclohexanone oxime synthesis zone is higher than 0.7 mol/l. 9.Process according to claim 8, characterized in that the concentrationhydroxylammonium in the aqueous reaction medium entering thecyclohexanone oxime synthesis zone is higher than 1.0 mol/l.
 10. Processaccording to any one of claims 1 to 9, characterized in that the aqueousreaction medium and a stream comprising the cyclohexanone and theorganic solvent are contacted in countercurrent flow.
 11. Processaccording to any one of claims 1 to 10, characterized in that theorganic solvent is selected from the group consisting of benzene,toluene, xylene, methylcyclopentane, cyclohexane, and mixtures thereof.12. Process according to any one of claims 1 to 11, characterized inthat, the phosphate concentration in the aqueous reaction mediumentering the cyclohexanone oxime synthesis zone is higher than 2.0mol/l.
 13. Process according to any one of claims 1 to 12, characterizedin that the joint content of cyclohexanone and cyclohexanone oxime inthe aqueous reaction medium exiting the cyclohexanone oxime synthesiszone is below 0.2 wt. %.